Vapor generating and superheating operation



June 9, 1964 P s. DlCKEY 3,135,300

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29, 1951 '7 Sheets-Sheet 1 IN VEN TOR.

PAUL S. DICKEY gwmwiv ATTORNEY June 9, 1964 P. s. DICKEY VAPOR GENERATING AND SUPERHEATING OPERATION 7 Sheets-Sheet 2 Original Filed June 29, 951

OOOOOOOOOOO OOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOO s 0 0000000 000000 0000000 0 o COCO V UOO o O OO O o O o 0 0000000 000000 000000 0 O .O O O 2 3 4 C 0 D 0 0 T T T T 00 00000000 JUOOOOO OOO SECONDARY SUPERHEATER '4 PRIMARY SUPERHEATER 6 REHEATER OOOOOOO INVENTOR.

PAUL S DICKEY FIG. 4

June 9, 1964 P. s. DICKEY VAPOR GENERATING AND SUPERI-IEATING OPERATION 7 Sheets-Sheet 3 Original Filed June 29, 1951 AIR HEATER STEAM PRESSURE FINAL STEAM TEMP O O 0 O O O O O O o ECONOMIZER HOOD-00000 PRIMARY SUPERHEATER REHEATER SECONDARY SUPERHEATER GENERATING SECTION SUPPLY GAS FLOW PATH FIG. 6

INVENTOR.

PAUL S. DICKEY ATTORNEY June 9, 1964 P. s. DICKEY VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29. 951

7 Sheets-Sheet 4 33 151 Y B I @Y Wm W E R I I G O x o 52m 1 I R Wm E w V m w u ww l P l T M] mm R E n W I MC 0 m m a w 6 B E T W T L o w s 0 mm L /R R N N 0 F- R 4 T m D W m u m C 6 D O D ".3.- 2 m R o o O G O 00 w m 0 m w o o m O O H W 9 8 7 .5; mmzmnm m umk SEEM ZE BOILER LOAD (PER CENT) INVENTOR.

PAUL S. DICKEY BY 9 ATTORNEY FIG. 7

June 9, 1964 P. s. DICKEY 3,136,300

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29. 1951 AIR HEATER o o o o 0 o o o o o O ECONOMIZER O (OOOOOOO0O 7 Sheets-Sheet 5 FINAL STEAM TEMP PRIMARY SUPERHEATER SECONDARY SUPERHEATER GENERATING SECTION INVENTOR.

PAUL S. DIOKEY ATTORNEY Fm. 8 21 MA June 9, 1964 P. s. DICKEY 3,136,300

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29. 1951 7 Sheets-Sheet 6 zo 20A INVENTOR. PAUL S. DICKEY FIG. 9 Z4 ATTORNEY June 9, 1964 P. s. DlCKEY 3,136,300

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 2 9. 1951 7 Sheets-Sheet 7 TO f TURBINE TO fTuRBms "FINAL'STEAM REHEATED I T MP. T AM TEMP. 4

(I 2%: 2 3% i 65 9 66 8% I 3| :3 mm m 3, 32 e7 0:

SPRAY TYPE ATTEMPERATOR SPRAY TYPE ATTEMPERATOR TURBINE PRIMARY SUPERHEATER INVENTOR.

PAUL S DICKEY FI IO BY FROM GENERATING 85cm" ATTORNEY United States Patent 3,136,300 VAPOR GENERATING AND SUPERI-IEATING OIERATION Paul S. Dickey, East Cleveland, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Original application June 29, 1951, Ser. No. 234,169, now

Patent No. 2,985,151, dated May 23, 1961. Divided and this application Sept. 22, 1960, Ser. No. 57,686

5 Claims. (Cl. 122-479) This in a division of my application Serial No. 234,169 filed in the United States Patent Office on June 29, 1951, now Patent No. 2,985,151.

My invention lies in the field of steam power generation and particularly in the controlof steam temperature in connection with present day vapor generators. Practically all central station capacity presently being installed, or on order, in the United States has rated steam conditions above 800 p.s.i.g. and 800 FTT; the highest operating temperature being 1050 FTT at pressures from 1500 p.s.i.g. to 2000 p.s.i.g. and rated load of from 500,000 to 1,000,000 lb. per hr., with a large percentage employing reheat surfaces. The problems involved in the generation and close control of the properties of steam are quite different now than was the case at the time of the inventions in this field which are shown in the prior art.

Superheat temperature control is particularly desirable in the generation of steam for the production of electrical energy in large central station power plants.

In such plants the upper limit of superheat temperature is governed by the materials and construction of the turbine served by the steam. In the interest of turbine eificiency the temperature of the steam delivered to the turbine should be maintained within close optimum limits throughout a wide range of capacities.

As feed water temperatures progressively increase there is less and less work for the boiler proper, with the result that its convection heat-absorbing surface has disappeared to the point where the modern large utility unit consists of a water-walled furnace, a convection superheater, an economizer and an air heater. Furnace design is now centering around sufiicient water cooling surface to absorb the radiant heat and to achieve the required relatively low furnace exit gas temperatures.

With the superheating or resuperheating of the steam in one or more convection type heat exchange surfaces the size and cost of such surfaces becomes a material factor in the total cost of the unit and any improvement leading to a reduction in the size of superheaters becomes of considerable importance. Usually these surfaces must be made of expensive high-alloy tubing to satisfactorily handle the temperatures and pressures encountered. p

It is thus a prime desideratum, in the design of such a unit, to proportion the steam generating surfaces and the steam superheating surfaces to give the desired final steam temperature at rated load. At peak load, in

excess of the rated load, the final steam temperature will be in excess of that desired and correspondingly at lower ratings the steam temperature will not equal that desired. It is false economyto design the superheater for desired final steam temperature at peak load, for all loads below that value would then produce steam below the desired temperature. On the other hand, the design of the superheater to produce the desired final steam temperature at some rating below rated load would require an excessive cost of superheating surface and an excessive final steam temperature throughout the upper ratings, with consequent danger to the turbine, or the necessity of extracting some of the surplus heat from the final superheated steam.

3,136,300 Patented June 9, 1964 ice ture, but not exceed it, requires exceedingly careful proportioning of the heat absorbing surfaces both for generating steam and for superheating it. But even if the desired superheated steam temperature be just attained initially by very careful designing at rated load, the superheated steam temperature will vary during operation by reasons of changes in cleanliness of the heat absorbing surfaces. Slag will form and adhere to the heat absorbing surfaces in the furnace thereby reducing the effectiveness of such surfaces and raising the furnace outlet temperature of the products of combustion. Furnace outlet temperature will also change with percentage of excess air supplied for combustion, with the characteristics of the fuel burned, and. with the rate of combustion and the corresponding rate of steam generation. All of these things will therefore affect the temperature of the gases leaving the furnace and supplied to the superheater, whether the superheating elements are located in the furnace where they absorb heat by radiation from the burning fuel and products of combustion, or whether they are located beyond the furnace where they absorb heat by convection from the products of combustion only.

With the furnace volume, as well as the vapor generating furnace surface, and the vapor superheating surface, fixed and invariable, the possibility of satisfactorily controlling the final steam temperature lies in controlling the volume and temperature of the gases contacting the superheating surfaces. Total fuel and air supply are varied with demand or rating to provide desired steam flow output. Furnace temperature of the flame and products of combustion does not vary greatly with rating. This leaves the controllable variables, the volume and temperature of the gases entering the convection superheating surfaces. The volume, or mass flow rate, has been controlled in the past through by-passing some of the gas flow around the superheater surface. The temperature of the entering gases may be controlled by selecting the amount of generating surface to be" con-' tacted by the gases before they enter the superheater. It is also known to have spray attemperators or other heat absorbing means for the excess heat in the .final steam before the steam goes to a turbine.

For any given furnace, as load increases, the heat input is increased, but the rate of heat absorption does not increase as rapidly as the rate of heat input; therefore, the furnace leaving temperature will rise. With both the quantity rate and the temperature of the gases leaving the furnace increasing with load, it is apparent that a fixed surface convection superheaterwill receive a greater heat rate at higher loads than at lower loads and the heat transfer area is usually designed for the volume and temperature of leaving gases at rated load. Any further increase in heat release rate supplies to the fixed superheater surface more heat by gas volume and by gas temperature than it is designed for and a corresponding excessive final steam temperature is experienced. Correspondingly, at operation below the rated load the fixed superheater surface receives less volume and a lower temperature of gases leaving the furnace with corresponding lowering of final steam temperature leaving approximate a uniform value over a range of operating ratings at each side of the rated load value.

It is known to control the primary heat absorption in a radiant furnace by directionally controlling the firing as to the furnace surface in relation to the superheater surface. The known tangentially placed tilting burners allow a control of varying utilization of the furnace heat absorbing surface through the tilting of the burners. It is also known to use tilting burners in systems wherein the excessive heat in the upper ratings is absorbed by spray attemperation or is by-passed around the superheater by means of a by-pass damper; and to increase the heat rate which is directed at the superheater, relative to that which is directed to the generating surface, at the low ratings. Such controls may be accomplished in sequence, or with, or without, overlap at the normal operating point.

I purposely employ selectively distribution of load between vertically tiltable burners proportioning the application of heat as between steam generating surface and steam superheating surface at different loads. I vary the heat release direction and consequently the effective furnace absorption area. In other words, as rating falls I utilize proportionately less of the generating surface and thus tend to maintain the temperature of the gases entering the superheating surfaces more nearly constant than would otherwise be the case. This is accomplished by controllably tilting the vertically spaced, tangentially firing burners to the end of directionally applying'the heat of combustion to the generating surface in accordance with rating.

My present invention has as a primary object method and apparatus for operating, and controlling the operation of, such vapor generating units through the utilization of more advantageous indexes of heat availability to the convection superheater and of operation of the unit as a whole.

So far as I am aware no one has previously used the actual entering gas temperature as an element in method and apparatus for controlling steam final temperature on units of thetype under discussion equipped with tangentially firing tiltable burners. Attempts have been made to ascertain continuously the temperature within the superheater tubes near the entrance, near the exit and at intermediate locations. Attempts have also been made to obtain the temperature of the steam before it enters the convection superheater and to use this temperature measurement in conjunction with the final steam temperature, in controlling spray attemperators, gas by-passes, and the like. These methods and arrangements have not been entirely satisfactory. A considerable time and heat lag occurs in the heat transfer through the films and metal of the tube surfaces, and with rapid fluctuating heat release loads and temperature effects as caused by slagging or deslagging of the furnace walls with corresponding fluctuating variations in heat absorption of the generating surface as well as flame drift around the furnace, has introduced lags in final steam temperature control systems with corresponding hunting and over-shooting. Through the use of my invention I avoid these inaccuracies and adverse eifects by utilizing the actual furnace gas exit temperatures as an element in my control system to maintain final steam total temperature.

In the drawings:

FIGS. 1, 2 and 3 are somewhat diagrammatic sectional elevations of a vapor generating unit having primarily radiant generating surface and convection superheating surface.

FIG. 4 is a section taken along the line 44 of FIG. 1 in the direction of the arrows.

FIG. 5 is a section taken along the line 5--5 of FIG. 1 in the direction of the arrows and to a different scale.

' burner tilting.

FIG. 6 is a diagrammatic showing of a vapor generating unit and one form of control for the tilting burners.

FIG. 7 is a graph of characteristic values in connection with other figures of the drawing.

FIG. 8 is a diagrammatic showing of my invention in connection with tiltingiburners and a spray type attemperator.

FIG. 9 is another arrangement of tilting burner and spray at'temperator control.

FIG. 10 is a diagrammatic showing of my control system in connection with steam superheaters and reheaters.

FIGS. 1, 2 and 3 show in somewhat diagrammatic sectional elevation a typical vapor generator in connection with which I will explain my invention. FIG. 4 is a section, to somewhat different scale, along the line 4-4 of FIG. 1 in the direction of the arrows.

The generator is of the radiant type, having a furnace 1 which is fully water-cooled with the walls 2 of vertical closely spaced plain "tubes constituting the vapor generating portion of the unit. Products of combustion pass upwardly through the furnace 1 in the direction of the arrow, through the tube screen 3, over a secondary superheater surface 4, a reheating section 5 and a primary superheating surface 6. A tubular economizer section 7 follows the superheater 6 and in turn may be followed by an air heater.

While my invention is applicable to generating units employing fuel burned in suspension, such as gas, oil, or pulverized'coal, the most prevalent use at present of tilting burners is with pulverized coal.

The unit is fired with pulverized coal from four sets of corner located tangential burners, vertically-adjustable or tiltable through a range of approximately +30 to horizontalto 30. FIG. 4 diagrammatically shows the firing arrangement of the four corner burners at a given elevation or section. I have shown in FIGS. 1, 2 and 3 that each corner set has four vertically spaced burners, a total of 16 for the unit. I designate (FIG. 4)

. the four vertical sets by the reference characters 10, 11,

12, '13 and in general indicate that the four burners of a vertically spaced set are tiltable together, although it is possible that other combinations of the 16 burners may be had for relative movement.

FIGS. 1, 2 and 3 are substantial duplicates except for illustrating the effect upon furnace flame location of In FIG. 1 the burners are horizontally firing or at what I designate a zero tilt position. The general flame location is diagrammatically illustrated.

In FIG. 2 the burners are shown depressed or in a downward tilt of some 25 and it is evident that more of the generating wall surface 2 is contacted than was the case in FIG. 1.

In FIG. 3 the burners are illustrated as having an upward tilt of approximately 25 and it is here evident that a considerable lower portion of the wall generating surface 2 is not directly contacted by the radiant heat of the flame body.

These illustrations show how the flame body can be raised or lowered over a considerable distance to make use of more or less furnace heat absorption surface and thereby proportion the amount of heat subjected upon the generating surface compared to that subjected upon the superheating surface and thus effecting wide range control over the gas temperatures leaving the furnace at the screen tubes 3; By thus providing control of furnace 7 heat absorption the eifect is similar to that which would be accomplished by the ability to increase or decrease the size of the furnace surface at will relative to a fixed convection superheating surface.

An upward tilting of the burners tends to increase steam temperature while a downward tilting tends to re-' and to consequently increase or decrease the temperature of the gas entering the superheater.

I have found that a most desirable index of heat available to superheat the steam is a continuous measure of the temperature of the gases immediately prior to their contacting the superheating surface. In a unit of the size and type being described the temperature of the gases first contacting the convection superheating surface should be in the neighborhood of 2000 F. for a steam final temperature of 1000 FTT and under different conditions of operation will be in the range of 17002300 F. When there is a change in furnace exit gas temperature, for any reason, there is of necessity a time lag of heat transfer and metal temperature stabilization before the gas temperature change is reflected in final steam temperature change. Thus the use of actual gas temperatures prior to convection heat exchange as an operating guide or control index anticipates the effect of the gas temperature change upon the superheating of the steam.

entrance to primary superheater 6; and E is between the primary superheater and the economizer 7. I expect that the gas temperatures at locations A or B will be in the range 1700-2300 F. while at location C, D or E the gas temperatures will be in successively lower ranges as the heat of the gases is transferred to the steam.

I preferably employ a radiation sensitive device at cations A and B and will refer to a bolometer as satisfactorily representative. The bolometer of the Rutherford et al. Patent 2,524,478 has been successfully used as a device sensitive to total thermal radiation for pro.- ducing an effect representative of the energy level of radiation received. The patent to English et al. No. 2,624,012 dated December 30, 1952, discloses and claims a circuit including the bolometer for actuating a recordercontroller in terms of temperature.

In FIG. 5 I show somewhat diagrammatically a section taken through the unit of FIG. 1, along the line 55, in the direction of the arrows. The locations A, B, C and D are not necessarily spot locations but are areas or planes between the various heat transfer surfaces. At I designate a bolometer or other radiation receptive head sighted across A and at 16 a similar head sighted across B. These devices may preferably operate in the range 17002300 F. I have also found that bare metal thermocouples or high velocity thermocouples may be used to obtain gas temperatures in locations A and B if proper precautions are taken against the corrosive, and erosive effects of the gases and entrained solid matter.

By way of example I illustrate in FIG. 5 four bare metal thermocouples TC-l, TC-2, TC-3 and TC-4 spaced across the area A in front of the screen tubes 3. These are preferably spaced across the screen tubes 3 and are connected in series with each other in a measuring bridge network to obtain an average of the temperatures to which they are subjected. Preferably the thermocouples are suspended downwardly through the roof of the unit until the thermocouple ends are in a line across the entrance to the screen 3 at about location A of FIG. 1. The thermocouple itself is encased in a thin wall protecting tube to protect it against the erosive and corrosive action of the gases but may under certain conditions be bare. When encased in a thin tube protector the latter is fastened to, and suspended from, an alloy tube which encases the lead wires upwardly to, and through, the roof.

Such a construction has been found to have a reasonably long life and to satisfactorily obtain an accurate average of the temperatures across the location A.

A similar use of thermocopules may be had through the area B or the area C. In FIG. 5 I show an alternate possible construction where the thermocouples TC-10, TC-20, TC-30 and TC-40 are projected through, and horizontally from, the rear of the unit assembly on supporting pipes which additionally act as protectors of the lead wires.

Regardless of the type of temperature sensitive device, or its mode of installation, the result is to obtain the actual temperature of the gases rather than any metal temperature or steam temperature in the various locations.

Referring now to FIG. 6 I show therein in very diagrammatic form the gas flow path in relation to the different heat exchange surfaces.

At 20 I show a control drive arranged to tilt the set of four vertically spaced burners 10, preferably through an angle i30 from the horizontal. In this figure I have shown only a single vertically spaced set of burners 10 as representative of the four corner sets previously mentioned and shown in FIG. 4. It will be appreciated that the showing of FIG. 6 is diagrammatic and the control drive 20 may be considered as simultaneously adjustably tilting all four sets of burners 10, 11, 12 and 13.

In the present arrangement the bolometer 16 is sensitive to gas temperatures at location B and is arranged to activate a recorder-controller 22 continuously positioning the stem 23 of a pneumatic pilot valve 24 to establish in a pipe 25 an air loading pressure representative of the average temperature of the gases at location B. Y The pilot valve 23, 24 is of a known type as disclosed in the Johnson Patent 2,054,464 and is so arranged in the present disclosure that an increase in temperature at location B results in an increase in the air loading pressure within pipe 25.

The temperature of the gases entering the steam superheating surfaces is an index of the heat available for superheating the steam. Many factors may contribute to variation of temperature of the gases entering the convection heating surfaces. Change in demand, with consequent increase or decrease in fuel-air admission rate will change the gas mass flow as well as its velocity and temperature. As an index of demand I show a Bourdon tube 21, sensitive to steam pressure, and arranged to position a pilot valve 21A to control total fuel and air supply rate. The demand index may be rating, such as steam flow rate or air flow rate, and may include a basic tilting of the burners in accordance with demand or load upon the unit. For steady state demand, the furnace exit gas temperature may vary from such causes as flame waver resulting in varying generating surface absorption, slagging or deslagging of generating surface, burnability of the fuel, etc. Regardless of the cause of the variation, the fact remains that a variation in such temperature may cause an undesired deviation in final'steam temperature from the desired value.

The temperature of the gases at the entrance to the superheating surface is therefore a cause index ma-v terially in time advance of any effect index such as metal or steam temperature of the superheating surfaces; By utilizing such cause index I may anticipate its effect upon the final steam temperature and provide an initial coarse adjustment to be verniered by final steam temperature toward the desideratum.

Referring again to FIG. 6 I show therein at 28 a' recorder-controller of final steam temperature arranged to position the movable element 29 of a pilot valve 30 continuously establishing in a pipe 31 a fluid loading pressure representative of 'final steam temperature. In the example being described, it is desired to maintain a final steam temperature of 1000 FTT as nearly constant as possible regardless of demand. It will be understood that the genteristics of such a radiant furnace generator with convection heated superheating surfaces predicates a tendency toward excessive final steam temperature for peak load and a deficiency in final steam temperature for loads below the design rated value.

In FIG. 7 I show the characteristic curve of such a convection superheater designed for final steam temperature of 1000 FTT under rated load operation. From FIG. 7 it will be. seen that desired control operation is'to remove the possibility of excessive steam temperature at the higher ratings and to raise the deficient steam tem perature at lowerratings. In general I accomplish this by removing excessive heat through spray attemperation while, at the lower ratings, I raise the characteristic temperature through proportioning the generating and superheating surfaces by tilting the fuel burners.

It will be seen that the air pressure loading line 31 joins the A chamber of a standardizing relay 32 which may be of the type described and claimed in the Gorrie Patent Re. 21,804 and whose output communicates with a pipe 33. Such a relay provides a proportional control with reset characteristics. It provides for the final control index (final steam temperature) a floating control of high sensitivity superimposed upon a positioning control of relatively low sensitivity. A function of the adjustable bleed connection in the relay 32 is to supplement the primary control of the pressure effective in pipe 31 with a secondary control of the same or of different magnitude as a follow-up or supplemental action to prevent overtravel and hunting.

The output of the relay 32, available through the pipe 33, is admitted through an adjustable bleed valve to the C chamber of an averaging relay 34, to the A chamber of which is connected the pipe 25. The relay 34 may be of the type described and claimed in my Patent 2,098,913.

The output of relay 34 is available in a pipe 35 through a manual-automatic selector valve 39 preferably of the type disclosed in the Fitch Patent 2,202,485 to the control .drive 20. The manual-automatic selector valve 39 provides a possibility of hand or automatic control of the tilting burners.

The operation of FIG. 6 is as follows. It will be understood that the response rate of bolometer 16 and its recorder-controller 22 may be adjusted to rapidly fluctuating gas temperatures to produce an averaging effect, if desired. Assuming a steady state of operation, an increase in temperature at location B indicates an increase of heat available for superheating the steam and under steady state operation it may be assumed that such an increase would cause an undesirable increase in steam final temperature. Thus I provide that an increase in temperature at location B will increase the loading pressure value within pipe 25 and within the A chamber of relay 34; This produces an increase in pressure within the D chamber of relay 34 and thus in the pipe 35. Preferably, an increase in pressure in pipe 35 actuates the control drive 20 to tilt the burners downwardly thus increasing the heat absorption of the generating surface and abstracting some of the available heat from the furnace gases prior to their reaching location B.

The componentsof the system may be so adjusted that, after the burners have been tilted downwardly to the predetermined maximum amount, the travel of control drive will cease.

Assuming for the moment that the temperature of the entering gases at location B is unvarying, then an. increase in final steam temperature results in an increase in air loading pressure in pipe 31 and in the A chamber of relay 32, and correspondinglyin pipe 33 which joins the C chamber of relay 34 through an adjustable restriction. An increase in air loading pressure in the C chamber of relay 34 acts in the same direction as an increase in air 8 pressure within chamber A and, as previously explained, results in a downward tilting of the burnersltl.

Conversely, a decrease in gas temperature at location .B, or 'adecrease in final steam temperature, results in an upward tilting of the burners 10 to decrease the generating surface heat absorption and raise the temperature of the gases entering the superheating surface.

Referring now to FIG. 8 I show therein an arrangement similar to that of FIG. 6 utilizing a spray attemperator between the primary superheater 6 and the secondary superheater 4 to remove excess heat from the steam. The function (FIG. 7) of the attemperator is to prevent final steam temperature from rising above the desired value at peakloads. With the arrangement of FIG. 8 all of the gases are allowed to pass through the superheating surfacebut some of the excessive heat in the steam is extracted by spray attemperation between the superheaters.

As shown in FIG. 8 the pipe 36 leads to a diaphragm actuated control valve 40 for controlling the flow of attemperating water through a pipe 41 to an attemperator 42 serially located between the primary superheater 6 and the secondary superheater 4 in the fluid flow path. The attemperator 42 is preferably of the type described in the patent to Fletcher et al. No. 2,550,683 wherein the superheated steam conduit has therein a Venturi acting as a part of a thermal sleeve to protect the conduit against thermal stresses. Forwardly of the entrance of the Venturi is a spray nozzle through which water is atomized in a conical spray which is enveloped by the high velocity superheateds-team. The nozzle is thus disposed in a relatively low velocity zone so there is a low pressure loss due to turbulence created by the nozzle body. The water leaves the nozzle in the form of a spray cone with a hollow vortex, the outer limits of this cone being within the entrance surfaces of the Venturi.

In FIG. 91 show an arrangement in some respects similar to that of FIG. 8 but incorporating refinements thereover. The control of the four corner sets of tiltable burners 10, 11, 12 and 13, by way of their separate control drives 20, 20A, 20B and 20C, is conjointly under the dictates of the gas temperature controller 22 and the final steam temperature controller 28, as in FIG. 8. The pipe 37, beyond the manual-automatic selector valve 39, is branched as at 45, 46, 47 and 48 to the four control drives. I may locate in each of the branches a manualautomatic selector valve 49 and through the agency of these four selector valves I may bias one or more of the vertical sets of burners relative to the other sets or may adjust any of the sets individually by remote manual means. a

In this embodiment I introduce a measure of the fiow rate of the water passing through the conduit 41 to the attemperator 42. Positioned in the pipe 41 is an orifice 50 for producing a pressure differential representative of the fluid flow rate and to which pressure difierential a water flow rate meter 51 is continually responsive. The meter 51 positions themovable element 52 of a pilot valve 53 continuously providing in a pipe 54 a fluid loading pressure representative of the flow rate of water to the attemperator 42.

I provide at 55 differential standardizing relay to the A chamber of which is connected the pipe 35 carrying the output of averaging relay 34. To the B chamber of relay 55 I connect the pipe 54 thus providing that the relay 55 is subjected to the difierential action of the loading pressures within pipes 35 and 54 respectively.

The output of relay 55 is available through a pipe 56 to the positioner 57 of a control valve 40. Each of the control drives 20, 20A, 20B and 200 are provided with response friction, capacities, and the like between the different control elements. Adjustments are provided whereby the control elements may be biased one relative to the other if desired.

In the system of FIG. 9 I introduce the water flow rate index to take car of feed pump variations, etc., which may otherwiseaifect the amount of water supplied to the attemperator 42 for any given control pressure subjected upon the pipe 56. In other words, the water flow rate index provides a tie-backto insure that the correct amount of water is used for spray attemperation to accomplish the purpose desired. 7

The relay 55 receives in its A chamber a loading pressure representative of desired water valve positioning called for by the indexes, gas temperature and final steam temperature. To this loading pressure is opposed the loading pressure representative of water flow rate, subjected upon the B chamber of the relay 55, to the end that if the water flow rate is as desired, the two loading pressures will tend to neutralize each other and no change in the loading pressure Within the pipe 56 will be made. If, however, the pressure in chamber A or that in chamber B deviates, then the differential between the pressure effects in the chambers A and B will be effective to vary the loading pressure within the pipe 56, effective in posi tioning the valve 40, until the increased or decreased rate of flow of water through the pipe 41, acting through the flow meter 51 and pipe 54 again brings the relay 55 to a balance condition.

Refer now to FIG. 10. In FIGS. 1, 2, 3, and 6 I have indicated areheat superheating surface 5 located (in the gas path) between the secondary superheater 4 and the primary superheater 6. In FIG. I illustrate my invention as applied to the control of the final temperature of the reheated steam as well as to the final temperature of the original steam. The drawing shows at the left-hand side the fiow path of steam from the generating section through the primary superheater 6, the spray type attemperator 42, and the secondary superheater 4 to the turbine. On the right-hand side of the drawing I illustrate that steam returned from the turbine passes through a controllable spray type attemperator 60 before entering the reheater section-5. Water to the attemperator 60 is furnished through a pipe 61 under the control of the regulating valve 62. It will be understood that the vapor passing through the reheater 5 does not necessarily have to be the same vapor that passed through superheaters 4 and 6, but may come from any source.

In general, the spray type attemperator 42 is under the conjoint control of the gas temperature controller 22 and the final steam temperature controller 28 in manner similar to that described in connection with FIG. 8. The spray type attemperator 60 is under the control of the gas temperature controller 22 and the reheated steam temperature controller 63.

The controller 63 is arranged to position the movable element 64 of a pilot valve 65 continually establishing in a pipe 66 a fluid loading pressure representative of final reheated steam temperature leaving the reheater section 5. Pipe 66 joins the A chamber of a standardizing relay 67 whose output pipe 68 joins the C chamber of an averaging relay 69. The pipe 25 from the gas temperature controller 22 joins the A chamber of the relay 69. Thus the relay 69 provides in its output pipe 70 a resultant fiuid loading pressure, the result of the pressures in pipes 25 and 68. The pipe 70 joins pipe 72 through manualautomatic selector valve 73 to the control valve 62.

I have shown in FIG. 10 that the control drive 20 (representative of power means for tilting all sets of burners) receives its air loading pressure from a pipe 71, through selector device 39, from a selective relay 95.

With this arrangement the burner tilting is selectively under the control of either final steam temperature or reheated steam temperature.

The tilting of the burners is primarily to raise steam temperatures at lower ratings and it is possible that either the final steam temperature or the reheated steam temperature is suificiently high that, were it the sole dictator of burner positioning, the signal would call for a depres sion of burner tilt. Such action would tend to reduce both final temperatures, thus further. lowering the one that was already too low. It would be better to raise both, thus bringing'the low temperature up toward desired value; the additional excess temperature of the already high one being taken care of byattemperation'or by-pass damper control.

The loading pressure of pipe 35 is subjected upon the A chamber of selective relay 95, while the loading pressure of pipe 70 is subjected upon the B chamber in opposition. Thus the two loading pressures act against opposite sides of diaphragm 96. The spring of relay is so adjusted that the relay force system is in balance when the two loading pressures are in balance and neither of the valves 97, 98 are open. The pipe35 joins the inlet of valve 98 while the pipe 70 joins the inlet a valve 97. The arrangement is such that whichever loading pressure is the lower, that is the one which is effective in establishing the pressure in pipe 71 to actuate control drive 20.

Assume that final reheated steam temperature 63 is lower than final steam temperature 28. The pressure in pipe 70 is less than that in pipe 35. Diaphragm 96 moves downwardly, opening valve 97, and admitting pres sure from pipe 70 to the D chamber of relay 95 and to the pipe 71. The pressure in 70 is the lower one 86 that pipe 71 is always receptive of the lower pressure 'of pipes 35 or 70.

The various devices of FIG. 10 may be so adjusted that valves 40 and 62 as well as drive 20 are sequentially effective in operation along the characteristic curve of FIG. 7.

The control system which I have illustrated and described finds, at the moment, its widest applicability in the burning of pulverized fuel but is equally effective in connection with vapor'generating and superheating units adapted to be fired by any fuel burned in suspension including gas or vaporized oil. j

While I have described in detail arrangements incor-' porating a continuous determination of gas temperature at location B through the agency of a bolometer, it will be appreciated that I contemplate the use at location B of any temperature sensitive device or devices which provide a continuous determination of the temperature of the gases available at the entrance to the superheating surfaces as clearly distinguished from any metal temperature or temperature of the steam or other fluid within the heat transfer surfaces. Furthermore, I contemplate that under certain conditions of operation it may be highly desirable to utilize in my method and control apparatus a determination of temperature of the gas flowing stream at other locations, for example, at A, C, D or B.

What I claim as new and desire 'to secure by Letters Patent of the United States is:

1. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end portion thereof, fired with one or more fluent streams of fuel and air through fixed location into the combustion chamber spaced vertically downwardly from the heating-gas outlet, and having convection vapor superheating surfaces positioned beyond the combustion chamber outlet in the path of heating gas flow; the method of operation which includes varying the total fuel and air input rate in accordance with demand upon the unit, passing the generated vapor through a portion of the superheating surface on its way to a utilizer, returning vapor from the utilizer through a reheating portion of the superheating surface, and varying the direction of the fluent streams into the combustion chamber selectively from either final vapor temperature or final reheated temperature whichever is the lower and in an upwardly direction as the selected temperature decreases and in a'downwardly direction a the selected temperature increases.

2. The method of claim 1 including removing any excess heat from the superheated vapor to maintain an optimum predetermined final vapor temperature through attemperation of the vapor conjointly responsive to a determination of temperature of the heating gases entering the superheating surfaces and a determination of the final superheated vapor temperature, and removing any excess heat from the reheated vapor tomaintain an optimum predetermined final reheated vapor temperature through attemperation of the reheated vapor conjointly responsive to a determination of the temperature of the heating gases entering the superheating surface and a determination of the final reheated vapor temperature.

3. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end portion thereof, a vapor superheater and a vapor reheater, the combination of means supplying fuel and air for combustion in fluent form to the combustion chamber, tiltable burner means for discharging the fluent supply into the combustion chamber spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal directionally upwardly or downwardly relative to the heating gas outlet, first temperature measuring means of the vapor in the superheater, second temperature measuring means of the vapor in the reheater, selective means responsive to the said first and second temperature means selectively actuating the motive means responsive to the vapor temperature having the greatest deficiency relative to its optimum value and means responsive to said selective means for tilting said burner means upwardly as said selected temperature decreases and downwardly as said selected temperature increases.

4. The combination of claim 3 including third temperature measuring means of the gases at the combustion chamber outlet, a first attemperator for the superheated vapor, a second attemperator for the reheated vapor, means controlling the first attemperator conjointly responsive to the first and third temperature means in a direction to decrease the temperature of the superheated vapor upon an increase in the temperature of the combustion vice versa, and means controlling the second attemperator conjointly responsive to the second and third temperature means in a direction to decrease the temperature of the reheated vapor upon an increase in the temperature of the combustion gases or the temperature of the reheated vapor and vice versa.

5. In a vapor generating unit having a convection vapor superheater, a convection vapor reheater and a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end portion thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion chamber, tiltable burner means for discharging the fluent supply into the combustion chamber spaced downwardly from the heating gas outlet, motive means adaptive to tilt the burner means from horizontal direction relative to the heating gas outlet, means for producing a first control signal proportional to the temperature of the superheated vapor, means for producing a second control signal proportional to the temperature of the reheated vapor, means for producing a third control signal proportional to the temperature of the gases at the combustion chamber outlet, means under the joint control of said first and third control signals for producing a fourth control signal proportional to the algebraic sum of said signals, means under the joint control of said second and third control signals for producing a fifth control signal proportional to the algebraic sum of said signals, means for selecting the lower of the fourth and fifth control signals, and means under the control of the selected signal for operating said motive means in a direction to tilt said burner upwardly as the selected control signal decreases and downwardly as the selected control signal increases.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,699 Huet Dec. 12, 1933 1,949,866 Huet Mar. 6, 1934 2,100,190 Jackson Nov. 23, 1937 2,109,840 Gordon Apr. 1, 1938 2,363,875 Kreisinger et a1. Nov. 28, 1944 2,413,128 Wills Dec. 24, 1946 2,575,855 Mittendorf Nov. 20, 1951 2,575,885 Mittendorf Nov. 20, 1951 2,590,712 Lacerinza Mar. 25, 1952 2,640,468 Armacost June 2, 1953 2,649,079 Van Brunt Aug. 10, 1953 2,663,287 Armacost Dec. 22, 1953 

1. IN A VAPOR GENERATING AND SUPERHEATING UNIT OF THE TYPE HAVING A VERTICALLY ELONGATED FLUID-COOLED COMBUSTION CHAMBER WITH A HEATING GAS OUTLET IN THE UPPER END PORTION THEREOF, FIRED WITH ONE OR MORE FLUENT STREAMS OF FUEL AND AIR THROUGH FIXED LOCATION INTO THE COMBUSTION CHAMBER SPACED VERTICALLY DOWNWARDLY FROM THE HEATING-GAS OUTLET, AND HAVING CONVECTION VAPOR SUPERHEATING SURFACES POSITIONED BEYOND THE COMBUSTION CHAMBER OUTLET IN THE PATH OF HEATING GAS FLOW; THE METHOD OF OPERATION WHICH INCLUDES VARYING THE TOTAL FUEL AND AIR INPUT RATE IN ACCORDANCE WITH DEMAND UPON THE UNIT, PASSING THE GENERATED VAPOR THROUGH A PORTION OF THE SUPERHEATING SURFACE ON ITS WAY TO A UTILIZER, RETURNING VAPOR FROM THE UTILIZER THROUGH A REHEATING PORTION OF THE SUPERHEATING SURFACE, AND VARYING THE DIRECTION OF THE FLUENT STREAMS INTO THE COMBUSTION CHAMBER SELECTIVELY FROM EITHER FINAL VAPOR TEMPERATURE OR FINAL REHEATED TEMPERATURE WHICHEVER IS THE LOWER AND IN AN UPWARDLY DIRECTION AS THE SELECTED TEMPERATURE DECREASES AND IN A DOWNWARDLY DIRECTION AS THE SELECTED TEMPERATURE INCREASES. 